There is known a flame-proof electric device, e.g. a flame-proof electromagnetic starter (cf. "Electrical Equipment for the Mining Industry", a brochure of Wallacetown, GB, pp. 3, 4) wherein the components of the electric circuitry of the device, e.g. contactors, control and protection units are accommodated within a flame-proof component chamber closeable with a lid providing access to the components of the electric circuitry for their maintenance and repairs. The design of the flame-proof electric device includes, in addition to the component chamber, two other flame-proof separate chambers, namely, the lead-in chamber for current conductors, intended for leading-in the power supply cable, and a chamber adapted to accommodate an interlocking disconnecting switch. The actuating or tripping mechanism of the interlocking actuating switch is mechanically connected with the lid of the component chamber in a way permitting the opening of the lid only with the disconnecting switch in the "off" state, i.e. With no voltage supplied to the functional components of the flame-proof electric device. The current-conducting cores of the power supply cable are electrically connected with the input terminals of the interlocking disconnecting switch via lead-through current-conducting terminals mounted on the flame-proof partition between the lead-in chamber and the chamber of the interlocking disconnecting switch. The output terminals of the interlocking disconnecting switch are electrically connected with the components of the electric circuitry of the flame-proof electric device via lead-through current-conducting terminals mounted on the flame-proof partition between the flame-proof chamber of the interlocking disconnecting switch and the flame-proof component chamber. The functional components of the electric circuitry of the flame-proof electric device are electrically connected with the current-conducting cores of a cable connecting the device with the power-receiving apparatus via a flame-proof electric connector accommodated in the flame-proof component chamber.
The flame-proof chamber of the interlocking disconnecting switch is closed with a lid providing access from the outside into this chamber for mounting the disconnecting switch, as well as for its inspection and maintenance.
The device of the prior art is of a complicated design, relatively big dimensions and weight, and its manufacture is complicated. This is explained by the necessity of providing a flame-proof partition with the lead-through current-conducting terminals between the flame-proof chamber of the disconnecting switch and the flame-proof component chamber, and by the successive arrangement of the flame-proof lead-in chamber, the flame-proof chamber of the interlocking disconnecting switch and the flame-proof component chamber, which necessitates the provision of lead-through current-conducting terminals on the respective spaced flame-proof partitions.
There is further known a flame- and explosion-proof electric device (GB, A, 1501818), comprising a flame-proof lead-in chamber intended for leading in the power supply cable, a flame-proof component chamber accommodating therein the functional components of the electric circuitry of the flame-proof electric device, the lid of the flame-proof component chamber, a flame-proof partition separating the flame-proof lead-in and component chambers, an interlocking disconnecting switch, a flame-proof chamber accommodating the interlocking disconnecting switch with at least one input terminal and at least one output terminal, at least one first lead-through current-conducting terminal mounted on the flame-proof partition and intended for electric connection of the current-conducting core of the power supply cable with the input terminal of the interlocking disconnecting switch, at least one second lead-through current-conducting terminal electrically connected with the output terminal of the interlocking disconnecting switch and the components of the electric circuitry, accommodated in the flame-proof component chamber, an actuating mechanism mechanically connected with the interlocking disconnecting switch and the lid of the flame-proof component chamber. The at least one second lead-through current-conducting terminal is accommodated on the lid of the chamber of the interlocking disconnecting switch, serving as the flame-proof partition between the flame-proof chamber of the interlocking disconnecting switch and the flame-proof component chamber.
The design of the last-described flame-proof electric device is also relatively complicated and involves difficulties in its manufacture, as it includes two spaced flame-proof partitions with lead-through current-conducting terminals. Moreover, the maintenance of the interlocking disconnecting switch is relatively difficult on account of the switch being accessible only upon the opening of the lid of the flame-proof lead-in chamber, disconnection of the cores of the power-supply cable and of the conductors in the flame-proof component chamber from the lead-through current-conducting terminals, and removal of the disconnecting switch from its chamber.